The 19th episode of the sixth season of "The Big Bang Theory" airs Thursday night at 8 p.m., ET, on CBS. If you cannot get to a television, you can also watch a live stream of the show online for free here, but please, click on that link at your own risk.

According to Hypable, last week's "Big Bang Theory" episode featured Leonard (Johnny Galecki) trying to figure out a way to encourage females to take jobs in the sciences. This was part of his role on a "Women in Sciences" committee at the university. Howard (Simon Helberg) and Sheldon (Jim Parsons) were also part of the committee, but seem less enthused about the project.

Eventually, though, Howard came up with the idea to talk to junior high school girls about their careers. The young ladies, however, were less than impressed. Leonard tried to be cool, and Sheldon revealed that the most famous female scientist, Marie Curie, poisoned herself on her own creation. Howard, meanwhile, showed off his astronaut outfit, but the students were not impressed that he only rode around in the rocket.

The three guys soon decided that their best bet was letting the girls listen to some female scientists. So, Sheldon and Howard called up their significant others, Amy (Mayim Bialik) and Bernadette (Melissa Rauch), who were playing hookey for the day at Disneyland. Ironically, the duo decried society's emphasis on feminine looks over smarts while they were each dolled up in princess outfits.

Meanwhile, the fourth member of the "Big Bang Theory" quartet, Raj (Kunal Nayyar), spent the episode on a date with the equally socially awkward Lucy (Kate Micucci). The two decided to limit the verbal interaction as much as possible by going on a texting date in the library. The day seemed to go well, though Lucy freaked out and ran away before she could kiss Raj on the lips.

While the date ended on a poor note, it does seem that Raj and Lucy will continue to interact in future episodes. Micucci told the Hollywood Reporter last week that she will show up later in the season.

"I know I'll be coming back at some point, but I don't know what the plan is," she said. "I love working with Kunal, and we have a lot of fun."

On Thursday night, meanwhile, the focus will shift to Howard, who finds a letter from his long-lost father. The elder Wolowitz has never been seen on "Big Bang Theory" after he walked out on the family when Howard was a child.

"The letter first showed up when Howard was 18, and he never opened it," Helberg told TVLine this week. "Of course, Sheldon, out of the goodness of his heart, very innocently opens it to try to help Howard, and Howard freaks out a bit. He doesn't want to know what's in it."

Helberg and his fellow "Big Bang Theory" castmates were at PaleyFest this week, where they celebrated the series' continued success. According to the Futon Critic, the show is the season's top program among adults aged 18-34, the first time a CBS show has held that title since 1987.

The episode's B-plot, meanwhile, revolves around Leonard and his girlfriend Penny (Kaley Cuoco) hosting a fancy party for their friends.

Read More:

'Big Bang Theory' Season 6 Spoilers: Rumored Proposal And Raj To Get A Love Interest In Valentine's Day Episode 16 'The Tangible Affection Proof'

'The Big Bang Theory' Record: CBS Sitcom Smashes Ratings Chart With 19.25 Million Viewers

'Big Bang Theory' Season 6 Spoilers: What's Next For Penny And Leonard After 'I Love You?' [VIDEO]